In recent years, photographic film cartridges have been proposed in which the film strip is completely enclosed within the cartridge and the film is loaded into the camera by simply causing the cartridge film spool to be rotated in the unwinding direction. A motor drive in the camera would generally be used for this purpose. Simplicity in film loading is one reason for this arrangement.
A problem with this arrangement, however, is that, unlike prior conventional film cartridges, there is no film leader extending out of the cartridge to indicate that the film is unexposed. Consequently, arrangements have been proposed to provide a visual indication of the exposure condition of the film and also to prevent loading of exposed film into the camera. This is particularly useful if the photographer wishes to switch cartridges to a different film type midway through the film exposures in the first cartridge. Commonly assigned U.S. Pat. No. 4,994,833 and the applications cross-referenced therein are representative of such proposals. However, such arrangements have the drawback that they require specially designed cartridge configurations and special mechanical sensors built into the camera to determine the status of the film in the cartridge and implement the double exposure prevention.
In commonly assigned U.S. Pat. Nos. 5,030,978 and 5,032,854 film cartridges are disclosed that utilize a rotatable radial bar coded disc element to provide information about the film in the cartridge, such as film manufacturer, film type, etc. These patents describe apparatus and methods for reading the bar codes during rewind operation to position the spool and the associated bar coded disc at a particular angular position of the spool so as to align visual indicators on the cartridge that indicate the exposure condition of the film, e.g. unexposed, partially exposed or exposed. In the '854 patent, a simple locking feature is shown that holds the spool in the desired indicator position. These patents do not disclose any provision for enabling the camera to automatically prevent reloading of exposed film or of enabling reloading of partially exposed film to an available frame position without the use of the special cartridge configuration and mechanical sensors of the types considered in aforementioned patent 4,994,833.
Commonly assigned U.S. Pat. No. 5,321,455 shows apparatus and method for using the bar coded disc to sense the initial parked angular setting of the film spool and thereby determine the film usage condition as part of a film loading operation. In this disclosure, when a cartridge is inserted into a camera and the film loading operation initiated, the disc is rotated and a single bar code sensor is used to detect transitions between bar elements, in effect counting the number of elements passing under the sensor from the initial setting to some reference point on the disc. Knowing the general format of the code, e.g. an interleaved 2-of-5 code, certain ranges of element counts will uniquely indicate the initial angular (parked) setting of the disc. The patent shows an arrangement whereby four initial settings can be determined, "Fresh" (Unexposed), "Partial" (Mid-roll interrupt: MRI), "Exposed" and "Developed"(Processed). Although operable for its intended purpose, it has been found that the use of a single sensor arrangement that relies solely on the count of elements to provide the initial setting indication is not entirely satisfactory. Specifically, the ability to discriminate the element counts for all four ranges, and even for only three ranges if the Processed position is not used, is not as reliable as would be desired. Accordingly, it is necessary to provide a more reliable arrangement for dynamically, determining, during an initial film loading operation, the angular setting of the film spool to provide reliable discrimination among at least three and preferably four initial settings to give an automatic indication of the usage condition of the film in the cartridge. The importance of reliability is the fact that there is only one chance to read the disc correctly since, once the spool is moved, the initial setting of the cartridge is lost.